Clay pigeon and a method for the preparation thereof

ABSTRACT

Provided is a clay pigeon which is a saucer-shaped compressed piece of clay and one or more additives. One of the additives is a calcium-based compound which reduces the drying shrinkage of clay and stabilizes the clay, which is preferably limestone powder or mortar. The clay content is at least 50% and the additive content 5-50%, calculated from the dry matter of the clay pigeon. The clay pigeon may also contain another additive reducing drying shrinkage and a component improving the plasticity of the mass. Also provided is a method for preparing a clay pigeon, where clay, one or more additives, and optionally a component improving the plasticity of the mixture are mixed to form a mass. Water is added if necessary to improve the plasticity of the mass, the mass is fed into a mold in which it is compressed for a moment, and the clay pigeon is removed from the mold while still in a plastic state.

The object of the present invention is a target used in trap and skeetshooting which is known as a clay pigeon. The invention alsoincorporates a method for its preparation.

In trap and skeet shooting, saucer-shaped targets are propelled by meansof an ejection device past the location where the marksmen are. Themarksman's intention is to hit the target flying in the air by a shotfrom a shotgun. The shooting takes place from several different angleswith respect to the flight path of the target, and the marksman shootingthe best series is obviously the winner. In order for the interpretationof scored hits to be as unambiguous as possible, the target must clearlydisintegrate when the pellets hit it. Disintegration must take placeregardless of which part of the target the pellets hit.

On the other hand, the targets must withstand transportation to theshooting ranges, the roads leading to which are often in poor condition.The targets must also withstand the strain they are subjected to whenpropelled into the air by the ejection device. Therefore, the targetsare, on the one hand, required to withstand transportation and handlingwell, but on the other hand, they must disintegrate easily when hit by ashot.

The properties required of the targets have so far been achieved byusing as starting material a mass consisting of coal tar ("pitch") andlimestone powder. In this mixture, coal tar acts as binder and limestonepowder as a filler material. The coal tar content is usually about20-40%.

Targets containing coal tar have the obvious disadvantage that thepitch-containing dust formed in connection with the disintegration ofthe target contains an abundance of so-called polycondensated aromatichydrocarbons, among them carcinogenic substances such as3,4-benzopyrene. Coal tar is thus a carcinogenic substance. When spreadin the environment, pitch dust infiltrates into the groundwater, andthrough plants--as well as directly--both animals and humans are exposedto it. In addition to the pitch dust, larger pieces of the targetsremain on the shooting ranges, and as they disintegrate slowly, theyaccumulate and remain within reach of animals and spoil the landscape.The health hazards of the present targets arise not only in thesituation of use but also during the production process. When thetargets are compressed, the raw material mixture is heated to about150°-250° C., in which case substances hazardous to health are releasedas gases. Thus, the workers involved in the production process aresubjected to very strong exposure. Harmful substances obviously alsospread to the surroundings of the production plant.

In addition to environmental problems, the present targets have thedisadvantage that their manufacture in Finland is dependent on importedraw materials. Coal tar is not produced in Finland but must be procuredfrom abroad.

Finnish patent publication FI 58396 discloses a clay pigeon, where chalkhas been used as filler and petroleum resin as binder. Although thecarcinogenity of this binder may be somewhat lower than that of coal tarpitch, this substance is also toxic when deposited in the environment.

The targets used in shooting have also been made of clay on a smallscale. In this case the blanks were fired, as is typically done withceramic objects, to achieve sufficient durability for transportation andpropelling. The problem with targets made in this manner was that theywere too hard and did not disintegrate when shot at, but merelysustained holes and scratches. The firing is in addition extremelyexpensive in relation to the price of the raw materials. Targets made ofclay were abandoned when the target described above consisting of coaltar and limestone powder was developed some hundred years ago.

The object of the present invention is to eliminate the saiddisadvantages of the "pitch" and clay targets and to achieve a targetconsisting of non-toxic, natural substances which disintegrates in thedesired manner into several pieces when shot at. By combining the basicraw materials of the clay pigeon in the proportions described below, itwill be possible to make targets from clay without firing, which meansthat the pieces of the targets will soften and disintegrate when theycome into contact with water in the environment. Thus the raw materialsused in the clay pigeons return to the soil without causing any damage.In addition to their environmental acceptability, the raw materials arereadily available and cheap, and thus the product relating to theinvention can easily also be made competitive pricewise.

The object of the invention is, therefore, a clay pigeon which is asaucer-shaped compressed piece made of clay and one or more additives.According to the invention, one of the additives is a calcium-basedcompound which reduces the drying shrinkage of clay and stabilizes theclay. The clay content is at least 50% and the additive content 5-50%,calculated from the dry matter of the clay pigeon.

The object of the invention also comprises a method for preparing theclay pigeon, characterized in that

--clay, one or more additives, and possibly a component improving theplasticity of the mixture are mixed to form a mass

--water is added if necessary to improve the plasticity of the mass

--the mass is fed into a mould in which it is compressed for a moment,and

--the clay pigeon is removed from the mould while still in a plasticstate.

The clay pigeon relating to the invention is, therefore, based onreadily available clay to which a calcium-based compound reducing thedrying shrinkage of clay and stabilising the clay is admixed as oneadditive. The calcium-based compound is a suitably inorganic calciumcompound such as calcium carbonate, calcium hydroxide, calcium oxide orcalcium sulphate (gypsum). In practice, suitable additives are, forexample, limestone powder or mortar, preferably limestone powder.

The biggest problem in using clay is its characteristic shrinkage whichoccurs during drying, known as drying shrinkage. Drying shrinkage iscaused by water being removed and may exceed 10% in Finnish clays. Highshrinkage causes the stability of the shape of the drying object todeteriorate. A precise shape is important for the reliability of use.Although the above-mentioned calcium-based compound reduces the dryingshrinkage of clay, to eliminate the problem further, another additivereducing the drying shrinkage of clay may also be added. Suitablematerials for this purpose are, for example, sand or other fine-grainedsoil type, crushed brick, power plant ash, sawdust, expanded clay,metallurgical crushed slag, crushed refuse ore from the mining industry,or chamotte.

The humidity of the mass to be moulded is maintained preferably at15-30%. The best results have been achieved with the humidity of themass to be moulded at 18-23%. In practice, the aim is to use the type ofclay which has a water content giving the mass to be moulded a suitablehumidity content. If necessary, the humidity of the mass can, however,be regulated by adding or removing water.

Clay is the main component of the mass to be moulded. Therefore,calculated as dry matter, clay makes up at least 50% of the dry matterof the mass. The additive content is preferably 5-50% of the dry matterof the mass.

When limestone powder and sand are used as the additives reducing dryingshrinkage, the limestone powder content is preferably 10-40% and thesand content 0-25% of the dry matter of the mass. If only limestonepowder is added to the clay, and no sand or other additive reducingdrying shrinkage, it is preferable to use 20-40% of limestone of the drymatter of the mass.

According to one embodiment of the invention, the limestone powder canbe replaced by mortar. Suitable mortar contents range between 5-25% andsand contents between 0-45% of the dry matter. Best results have beenobtained using 5-10% mortar and 25-40% sand of the dry mass.

According to one embodiment, the mass used for preparing the claypigeons also contains a component improving the plasticity of the mass.As the component improving plasticity can be used, for example,lignosulphonate or starch. Lignosulphonates are a component of the wasteliquor produced in pulping which originates in the lignin contained bywood. It has been found that lignosulphonates improve the dispersionproperties of clay particles, thus maintaining good plasticity of theclay, even when the water content of the mass to be moulded is reduced.

The amount of the component improving plasticity is preferably 0.4-1% ofthe dry matter of the total mass.

The above requirements placed on targets used in trap and skeet shootingcan be met with various material combinations, and thus it should benoted that the above additives, that is, limestone powder or mortar andsand only serve as examples.

From ceramics it is known to add to clay components reducing dryingshrinkage, such as sand and other finely crushed substances. Whilereducing drying shrinkage, these substances at the same time weaken thein itself strong structure of the clay, so that durable ceramic productscan only be obtained by firing. Of the clay-based raw material relatingto the present invention, end products can be made without firing.

Known targets using coal tar pitch or petroleum resin as binder are castinto moulds while hot, which means that the compressive force requiredis very low. The target is removed from the mould once the mass hascooled and hardened. The removal can then be easily done by means ofejectors, because at this stage the target withstands mechanical strainwithout its form suffering. Cooling to the temperature for removal takessome tens of seconds.

The clay-based targets relating to the present invention cannot beprepared or removed from the mould in the manner described above. Whenthe material mixture to form the clay pigeon is fed into the mould it isnot a flowing liquid but a plastic mass. The moulding pressure requiredfor the moulding is so high that the mass adheres easily to the mould.The mass also hardens relatively slowly and usually takes several days.Therefore, the mass cannot be left in the mould to harden but the claypigeon must be removed from the mould while still in a plastic state.Final hardening takes place during storage. These facts, that is, thetendency of the mass to adhere to the mould and the removal of the claypigeon from the mould while in the plastic state place considerabledemands on the removal technique. Mechanical ejectors cannot be usedwithout the shape of the target suffering.

A clay pigeon in the plastic state can be removed, for example, by meansof the following methods or combinations of them:

According to one embodiment, the removal is carried out by blowing airbetween the mould and the clay pigeon formed.

According to another embodiment, the removal is carried out by opening amould divided into sectors and constructed to be opened.

According to yet another method, the removal is carried out by reducingthe contact surface between the mould and the clay pigeon so that a partof the mould's surface is detached from contact with the clay pigeon. Afeasible solution in practice is disclosed below in connection with thedescription of the drawings.

The removal of the clay pigeon from the mould can be facilitated byheating the mould before removal. As a result of the heating, thesurface of the clay pigeon hardens more rapidly, thus making it lesssusceptible to damage. Due to the drying of the surface of the claypigeon, removal from the mould also becomes easier.

Adhesion of the mass to the mould can be reduced or completely preventedby partly or completely greasing or covering with film that surface ofthe mould which is in contact with the clay pigeon.

A mould practicable for use in the preparation method relating to theinvention is described in greater detail in the following, withreference to the appended drawings in which

FIG. 1 shows a cross-sectional side view of the mould used in thepreparation method relating to the invention

FIG. 2 shows the mould of FIG. 1 according to another embodiment.

In FIG. 1, reference number 10 refers to the bottom part of the mouldand number 11 to the top part. Parts 10 and 11 of the mould can be movedwith respect to each other. The mould 10, 11 is preferably of metal,hard plastic, or any other material that withstands the requiredmoulding pressure, on which can be given a smooth surface by turning.The space 12 between the bottom part 10 in its lowest position and theupper part 11 corresponds to the shape of the undried and unshrunk claypigeon. The shape of the concave surface 13 of the top part 11 gives thesurface of the target its final shape. The part 16 between the outerring 14 of the clay pigeon and the centre part 15 is provided with astepped construction 17, to prevent ricochets. The mass is fed into themould while the mould is open and the top part 11 is then lowered andthe required moulding pressure is exerted on it. According to oneembodiment, both the bottom part 10 and the top part 11 are furnishedwith channels 20 and 21 for air. The removal of the clay pigeon may becarried out so that air is first blown through the channels 20 of thebottom part, in which case the clay pigeon formed will detach from theconvex surface of the bottom part. The top part 11, to which the claypigeon has adhered, is then lifted up. The top part 11 with the claypigeon is lifted onto a storage plate on which the clay pigeon is placedonce it has been removed from the top part 11 by blowing air through thechannels 21. The mould parts 10, 11 may be heated, preferably in thevicinity of the surfaces of the clay pigeon.

If the surface of the mould is provided with a film, the removal of theclay pigeon can be carried out by means of this alone.

FIG. 2 shows another embodiment of the mould of FIG. 1, according towhich removal can be carried out by reducing the contact surface betweenthe mould and the clay pigeon so that a part of the mould's surface isdetached from contact with the clay pigeon. The top part 11 is dividedinto ring-like parts 30, 31 which are capable of moving in the verticaldirection in relation to each other and in relation to the centre part32. These moving rings can be used to remove the clay pigeon from thetop part 11 of the mould. Removal can be carried out, for example, bypressing the rings 30, 31 down with respect to the centre part 32, inwhich case the surface of the centre part of the target is forced todetach from the surface of the centre part 32 of the top part 11 of thecorresponding mould. According to another embodiment, the rings may belifted up, thus detaching their contact surface from the clay pigeon.

It is obvious to a person skilled in the art that the differentembodiments of the invention may vary within the scope of the claimspresented below.

We claim:
 1. A clay pigeon which is a saucer-shaped compressed piececomprising clay in an amount of at least 50% by weight calculated fromthe dry matter of the clay pigeon, and an additive in an amount of 5-50%by weight calculated from the dry matter of the clay pigeon, whereinsaid additive is a calcium-based compound which reduces the dryingshrinkage of clay and stabilizes the clay.
 2. A clay pigeon as claimedin claim 1, wherein the additive is limestone powder or mortar.
 3. Aclay pigeon as claimed in claim 1, further comprising a second additivewhich reduces the drying shrinkage of clay.
 4. A clay pigeon as claimedin claim 3, wherein the second additive which reduces drying shrinkageis sand, a fine-grained soil, crushed brick, power plant ash, sawdust,expanded clay, metallurgical crushed slag, crushed refuse ore from themining industry, or chamotte.
 5. A clay pigeon as claimed in claim 1,further comprising a component which improves the plasticity of themixture comprising clay and the additive.
 6. A clay pigeon as claimed inclaim 5, wherein the component which improves plasticity islignosulphonate.
 7. A method for preparing the clay pigeon claimed inclaim 1, comprising mixing the clay and additive to form a mass, feedingthe mass into a mold and compressing the mass, and removing the claypigeon from the mold while the pigeon is still in a plastic state.
 8. Amethod as claimed in claim 7, further comprising mixing a componentwhich improves plasticity with the clay and additive.
 9. A method asclaimed in claim 7, further comprising adding water to the mixture ofclay and additive to improve the plasticity of the mass.
 10. A method asclaimed in claim 7, wherein removal is carried out by blowing airbetween the mold and the clay pigeon.
 11. A method as claimed in claim7, wherein removal is carried out by opening a mold divided into sectorsand constructed to be opened.
 12. A method as claimed in claim 7,wherein removal is carried out by reducing the contact surface betweenthe mold and the clay pigeon so that a part of the surface of the moldis detached from contact with the clay pigeon.
 13. A method as claimedin claim 7, wherein removal of the clay pigeon from the mold isfacilitated by heating the mold.
 14. A method as claimed in claim 7,wherein adhesion of the mass to the mold is reduced by partly orcompletely greasing or covering with film that surface of the mold whichis in contact with the clay pigeon.
 15. A method as claimed in claim 7,wherein adhesion of the mass to the mold is completely prevented bypartly or completely greasing or covering with film that surface of themold which is in contact with the clay pigeon.